1. Field of the Invention
This invention relates generally to an apparatus for pulling fastener pins through a workpiece and particularly relates to a nose assembly having a set of internally-supported spring-biased jaws for engaging a series of pull grooves formed on the fastener pins.
2. Description of Prior Developments
Pin and collar fasteners of the lock bolt variety are commonly used to fabricate various frames and structures including aircraft wings and aircraft cabins. It is often desirable to produce an interference fit between the body of the pin and the members being fastened in order to produce a fatigue resistant joint by cold working the material surrounding the pin. This is particularly advantageous in the case of a fabrication requiring a leak-tight assembly such as an aircraft wing which also serves as a fuel tank, or an aircraft cabin which is subject to pressurization. While an interference fit can be clearly desirable in numerous applications, there has been a most undesirable problem associated with the use of an interference fit between a fastener pin and its surrounding structure.
In order to produce such an interference fit, it has been necessary to use a hammer or an air impact tool to force the fastener pin through a hole formed through each member being fastened. This hammering has resulted in excessive noise levels reaching up to 120 decibels. Hammering poses a threat to hearing and requires the use of ear protection. Another drawback associated with such hammering is that it often damages the head of the fastener pin and/or the members being fastened.
Setting fasteners by conventional techniques requires one assembler to initially position the pin through one exposed side of the workpiece and subsequently hammer the pin therethrough while a second assembly worker applies reinforcing support to the opposite side of the workpiece via a bucking bar. Thus, two workers are needed to carry out this labor intensive task using conventional methods.
Prior to the present invention, no tool was available which could adequately grip the relatively short axial length of the fastener pin which projected through the members or workpieces being fastened. That is, a portion of the end of the fastener pin opposite its head is typically of reduced radial section to allow that section of the pin to be freely inserted through the members being fastened. This exposes a short axial portion of the fastener prior to reaching the point of interference between a radially enlarged portion of the pin shank and the opposite or back face of the structure being fastened.
Of course, it is possible to make the non-interference fit portion of the fastener pin longer to provide a longer gripping surface. However, this results in considerable expense and material waste since this portion, which is commonly known as a pintail, is broken off and discarded when a collar or nut is subsequently swaged or fastened over the pin. This poses a particular problem in aircraft applications since the material used for the fastener pins in such applications is frequently titanium which is quite expensive.
Moreover, it is often not possible to use long fastener pins due to space limitations which prevent a fastener tool from accessing the elongated fastener pins. This is particularly true in the case of aircraft applications where structural channel members known as "J stringers" prevent the fastener tool from reaching and engaging those fastener pins located within the Jstringer channels.
Accordingly, a need exists for a reliable nose assembly for use with a low noise level tool capable of gripping a short axial length of a fastener pin and quietly and smoothly pulling the fastener pin through an interference fit hole without damaging the fastener pin or the workpieces being fastened.